Print CSS Not Loading

I have two CSS files for print and screen. In screen.css:

..screen
{
font-weight:bold;
font-size:12px;
}

..print
{
visibility:hidden;
}

In the HTML:



>
href="screen.css" />


Text A
Text B font>

[etc.]

In print.css, the parameters are swapped. In other words, Text B will
show on the printed page, but not on screen, and vice-versa for Text
A.

But as it stands now, it's not quite working. On "screen," it looks
OK; hidden text is hidden, shown text is shown. When printed in
Firefox 2, though, the output looks no different from on "screen." I'm
stumped why this is, and so is everyone else I've shown this to. Any
ideas?